"But can't you envision the GOP nominating someone for whom you could not vote?"
Most definitely! My choices would then be whether the candidate would get a hold-my-nose vote or whether to vote write-in candidate or to not vote at all. Not being wired to not vote and have my voice heard, I would wrestle with the first two.
"A Dem (other than hillary :-)) might be an alternative."
The comments in my first post to you cover that situation. Can't ever see it happening, not in this current climate, as I don't think the dems are ever going to get a clue and nominate someone I could support.
Maybe they will. But what bothers me a lot is that the GOP is going way off track, and might nominate someone who is worse.
I think it would be easier to get the GOP back on track than it would be to get the Dems corralled, but it might take a wake-up call.